Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...

I tried this compact combination below during last session and found that although contrast increased, the image was too dark, requiring very high gain to achieve 25 - 30 ms shutter speed - not too useful at a focal length of 4600 mm at f/20. The PST was used without its collimating lenses.
Is this a lost cause?

It was inserted into the focuser as shown. Focus was easy to find. It definitely produced higher contrast images. However, as I was afraid, the image was dark and required a very high gain to achieve 26 - 30 ms shutter speed.

Are there any changes I can make to the components in the setup that could improve the image brightness? I would like eventually to use a 0.4Å
rear etalon but, for now, I'll play with what I have.

I have the snout of the PST etalon in the eyepiece holder on the Quark, so it's behind the Quark in the optical train as Mark mentioned. At this point, I'm literally just holding my eyepieces by hand against the PST etalon, but I have a few ideas on how I can actually mount them.

The view on inital testing was extremely dim. I could barely see the Sun at all. A few very tiny changes have made it much, much better.

First, I went through and made sure everything was square (the diagonal to the focuser, the telecentric to the diagonal, the Quark in the telecentric, etc). It was all very very small tweaks, but it made an immediate improvement.

Next was to rotate the PST relative to the Quark. The etalons polarize the light strongly, and I think there was a bit of light reduction here as a result. This was less of an improvement than getting everything square, but it did make an improvement (it may have been due to just continuing to make everything more square, though...I'm just not sure).

Finally, going back and playing with tuning the Quark and tuning the PST made the biggest improvement. I went back to -5 on the Quark, then tried adjust the PST tuning. Then -4, and adjust the PST. On and on, through every setting, until I found what worked best. Each and every Quark and each and every PST is different, so you'll need to test yours out. This made a huge, huge, huge difference--the Sun is easy to see now, as opposed to nearly invisible. I strongly recommend you pull the tuning ring off of the PST so you can tune it further in either direction than you can when the ring is mounted.